Two new papers reveal important insights into whales in the Northern Indian Ocean

Last week two new papers were published revealing important information about feeding and parasites in blue whales off Sri Lanka and humpback whale song off the Goan coast of India. Read the full abstracts of these papers below:

Press release: A study on the diet of Northern Indian Ocean blue whales has just been published in the journal Frontiers in Marine Science. The study revealed that while globally blue whale populations feed predominantly on Euphausiidae (krill), Northern Indian Ocean blue whales feed predominantly on Sergestid shrimps. This demonstrates that blue whales can locate and feed on dense swarms of other types of prey when they occur. Within the Indian Ocean, sergestids are present in the top 300 m of the water column, which correlates with the deep scattering layer in the area. This need to dive deeper in search of prey likely explains the prevalence of fluke up diving amongst blue whales in Sri Lankan waters relative to other parts of the world.

This study also found the presence of Acanthocephalan parasites in the stomach and intestines of the Northern Indian Ocean blue whales. While these parasites have previously been recorded in other ocean basins, this is the first record for this region. This finding highlights the need for further studies on parasitic flora and long-term monitoring of health of these cetaceans for their proper management and conservation.

The lead author, Dr. Asha de Vos, founder of The Sri Lankan Blue Whale Project the flagship project of Oceanswell was particularly excited about the implications of this finding. She said, “These findings highlight the need to continue long-term research efforts, study and evaluate species within their habitat ranges, understand their behavioural adaptations, and tailor-make management and conservation decisions based on their needs”. Co-author Dr. Simon Jarman from Curtin University and CSIRO further added, “Analysis of DNA from environmental samples can generate a lot of new ecological knowledge. This is a nice example of the sorts of information we can uncover with molecular analyses.” To learn more about this research please contact Dr. Asha de Vos; Founder, Oceanswell: asha@oceanswell.org

Abstract: For over two decades, passive acoustic monitoring (PAM) methods have been successfully employed around the world for studying aquatic megafauna. PAM-driven studies in Indian waters have so far been relatively very scarce. Furthermore, cetacean populations inhabiting the north western Indian Ocean are far less studied than those in many other regions around the world. This work likely constitutes the first systematic study of the vocal repertoire of humpback whales (Megaptera novaeangliae) at a near-shore site along the western coast of India. Analysis of the observed vocalizations provides an insight into the behaviour of the species. This is significant as it assists in developing a better understanding of the habitat use of the non-migratory Arabian Sea humpback whale population. In contrast, other breeding populations such as those around the North Atlantic, South Pacific and Australia have been relatively well studied. Underwater passive acoustic data were collected during March 2017 using an autonomous logger at a shallow-water site off the eastern edge of Grande Island off the coast of Goa. Humpback whale vocalizations were found to occur over multiple days in the recordings. Time–frequency contours of individual units of vocalization were extracted with the aid of an automatic detection technique and the characteristics of the units were measured. Further, successive units were analysed for formation of phrases and themes. Reconstruction of putative songs from the identified units and themes was not possible due to the limitations imposed by the nature of data collection. Detailed analyses of units, phrases and themes are presented.

This paper also discusses the relevance of this study in relation to the wider Arabian Sea humpback whale population: “Formal collaborative studies in the Arabian Sea region are in their early stages. Cursory comparison of vocalizations from this study with those collected off Oman from the same year provides some indication of shared themes (2017 email exchanges between S Madhusudhana and researchers S Cerchio, AJ Willson and MS Willson studying humpback whales along the coast of Oman; unreferenced, personal communication); however, this requires further dedicated analysis. These preliminary findings concur with comparison of historical song samples between Hallaniyat Bay in Oman and Sri Lankan side of the Gulf of Mannar that were found to have ‘virtually the same content’ (Whitehead 1985). Understanding regional transmission of song patterns is considered as a gateway to evaluating the connectivity between humpback whales in the Arabian Sea, and considered a priority for conservation management measures (Minton et al. 2015). Further collaboration on evaluation of song structure between these data-sets is warranted.”

Watch this space for the next steps in this exciting story that started with the recording of humpback whale song on both sides of the Arabian Sea in the early 1980s!